Industrial gas turbines generally include a plurality of combustors disposed in an annular array about an axial centerline of the gas turbine. Hot gases of combustion flow from each combustor through a transition piece and across a first-stage of stationary nozzles. Because the transition piece and the stationary nozzles are formed of different materials and are subjected to different temperatures during operation, each may experience different degrees of thermal growth as the gas turbine cycles through various operating modes. As a result, the transition piece and the first-stage of stationary nozzles may move radially, circumferentially and axially relative to one another. Also, similar relative movement may occur as a result of dynamic pulsing of the combustion process.
Typically, thermal growth variations are addressed by providing a gap between the transition piece and the first-stage of the stationary nozzles. In addition, one or more seals may be provided to seal the gap and thereby reduce cold air leakage into the hot gas path. However, due to the high pressure and temperature of the hot gas flowing across the gap, at least a portion of the hot gas may be ingested into the gap and flow against the seal, thereby degrading the seal over time.
One method for cooling the seal and for purging the hot gas from the gap includes flowing a purge medium such as compressed air into the gap at a pressure sufficient to purge the gap and/or cool the seal. Although this method is generally effective, larger gaps require a greater volume of the purging medium to affectively purge the gap. As a result, the greater volume of unburned and/or unmixed purging medium may increase the levels of undesirable combustion emissions such as, but not limiting of, nitrogen oxide (NOx) and/or carbon monoxide (CO). Thus, an improved system and method for recirculating the hot gas ingested into the gap would be useful.